Is the 18 month deadline based on the number of days or the number of months after the end of the taxation year?

When the corporation's taxation year ends on the last day of a month, the claim will be accepted as filed on time if it is delivered on, or the postmark on the envelope is for, the last day of the 18th month after the end of the taxation year.

When the last day of the taxation year is not the last day of a month, the claim will be accepted as filed on time if it is delivered on, or the postmark on the envelope is for, the same day of the 18th month after the end of the taxation year.